This application claims the priority of German Patent Document 100 01 486.0, filed Jan. 15, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method for controlling a gear unit of a motor vehicle having synchronizing devices.
German Reference DE 195 26 273 A1 discloses a gear mechanism which has synchronizing devices and in which the actuating path x of the synchronizing device is fed as operating signal to a control device. Information from the shifted gear step and the gear step to be shifted, is provided as a further operating signal to the control device from which the expected speed differential is determined. A shifting force is determined from a characteristic diagram as a function of the actuating path x and the speed differential, and adapted in the course of the synchronization operation.
Because of wear in the region of friction surfaces on the synchronizing device as the operating period of the synchronizing device increases, the operating point is displaced. Therefore, the use of the actuating path x is affected by error. Furthermore, it becomes clear that the service life of the synchronizing device is a function of the use of the motor vehicle. In particular, depending on use, some gear units experience mechanical impairments in the region of the friction surfaces, which can lead to impairment of the driving and/or shifting comfort, going as far as component failure, while other gear units exhibit no such impairments.
It is therefore the object of the present invention to propose a method for controlling a gear unit which ensures the functionality of the gear unit over a prescribed service life.
It has been found that the number of shifting events for the same kilometer reading differs for different motor vehicles. With a rising number of shifting events, there is a rise in the loading of the synchronizing device and a lowering of its service life. It is possible to determine a shifting frequency from an evaluation over an operating period. For example, the number of shifting events is determined over a prescribed distance or from the manufacture of the vehicle. It is also possible to evaluate the shifting events statistically. For example, as regards the operating period, it is possible to make an evaluation over a comparatively short operating period or a fixed driving distance or since the most recent beginning of a journey. This evaluation provides information, for example, on the heat budget of the synchronizing device, with the possibility of taking into account the information obtained for a favorable characteristic of the control signal and/or the shifting force. Alternatively, or in addition, the evaluation can be performed over a long operating period or a long driving distance, in particular from the manufacture of the vehicle. This evaluation provides information, in particular, on the state of the synchronizing device or the wear thereof.
If severe loading of the synchronizing device is indicated by the evaluation, the characteristic of the controlled variable, as well as the latter the characteristic of the shifting force can be suitably adapted. For example, given an indicated severe loading of the synchronizing device, the build-up of the shifting force can be slowed down, in particular within specific synchronizing phases, or its maximum can be limited.
According to another embodiment of the present invention, It has been found that the current inclination of the travel path influences the frictional conditions of the synchronizing device. For example, given comparable driving conditions, the torques to be picked up and transmitted by the synchronization device are different for an uphill roadway and a downhill roadway. These changed power conditions can be taken into account in accordance with a determined inclination when influence is exerted on the controlled variable. Consequently, larger shifting forces can be required given a uphill roadway, for example, in conjunction with the same period of a synchronization phase.
According to the present invention, the switching forces can be fashioned such that they always remain below the permissible continuous critical loads in conjunction with shifting times which are optimum for the respective driving situation.
Alternatively or in addition to the absolute value of the switching force produced, the control signal can be influenced to vary or adapt the characteristic of the build-up of the shifting force, in particular the period of the synchronization process.
The control signal is preferably determined taking account of the shifting events, in particular the shifting frequency, and the inclination of the roadway in order to obtain all of the abovementioned advantages.
In accordance with a further embodiment of the present invention, a control signal is determined within a (synchronization) phase, in particular the phase of the initial synchronization, the turning of the synchronization ring, the synchronization, the blocking, the turning back of (synchronization) phase, in particular the phase of the initial synchronization, the turning of the synchronization ring, the synchronization, the blocking, the turning back of the synchronization ring, the turning of the coupling body and/or the making of a self-closed connection. In particular, the determination is performed within Phase I until the synchronization point is reached, from the end of Phase I in a Phase II until the synchronization speed of the gearwheel with the assigned shaft has been reached and/or from the end of Phase II in a Phase III until the synchronization device ceases to be actuated.
The control signal is determined within at least one of these phases via a functional dependence which takes account the temporal sequence of the shifting events, their number or frequency and/or the topography of the travel path, in particular the inclination thereof. It is thereby possible to take specific account of the requirements placed on the shifting force in the individual synchronization phases of the synchronizing device.
The functional dependence can take any of several desirable forms. For example one form could be a function dependent on one of the parameters. Alternatively, evaluation is possible by means of a (multidimensional) characteristic diagram which specifies the control signal, the shifting force at discrete points or in ranges for the temporal sequence of the shifting events, their number or frequency and/or the inclination of the travel path.
Alternatively or in addition to the absolute (desired) value of the control signal, or an additional functional dependence can be used in order to describe an information item on the characteristic, in particular a rate of change (gradient) of the control signal.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.